Final results of the EDELWEISS-II WIMP search using a 4-kg array of cryogenic germanium detectors with interleaved electrodes

The EDELWEISS-II Collaboration has completed a direct search for WIMP dark matter with an array of ten 400-g cryogenic germanium detectors in operation at the Laboratoire Souterrain de Modane. The combined use of thermal phonon sensors and charge collection electrodes with an interleaved geometry enables the efficient rejection of γ-induced radioactivity as well as near-surface interactions. A total effective exposure of 384 kg d has been achieved, mostly coming from fourteen months of continuous operation. Five nuclear recoil candidates are observed above 20 keV, while the estimated background is 3.0 events. The result is interpreted in terms of limits on the cross-section of spin-independent interactions of WIMPs and nucleons. A cross-section of 4.4×¹⁰−8 pb is excluded at 90%CL for a WIMP mass of 85 GeV. New constraints are also set on models where the WIMP-nucleon scattering is inelastic.     

Looking for SUSY with EDELWEISS-I and-II

The latest results obtained by the EDELWEISS WIMP (weakly interacting massive particles) direct detection experiment using three heat-and-ionization 320-g germanium bolometers are given. Presently the most sensitive WIMP direct detection experiment for WIMP mass >30 GeV, EDELWEISSI is testing a first region of SUSY models compatible with accelerator constraints. The status and main characteristics of EDELWEISS-II, involving in a first stage 28 germanium bolometers and able to accommodate up to 120 detectors, are briefly presented, together with neutron background estimates.     

Radon-induced background and methods of its elimination in the EDELWEISS-II experiment

The EDELWEISS-II experiment is aimed at direct search for nonbarion cold dark matter. The important problem of the experiment is a decrease in the ²²²Rn background and its daughter products without which it is impossible to achieve a record sensitivity to the scattering cross section of dark matter particles. A highly sensitive radon detector has been developed by means of which the facility shield is optimized and the total gamma-background is halved. The detector is used in the EDELWEISS-II facility for continuous monitoring of the radon content in the process of data sampling that plays the key role for correct data interpretation.     

Monitoring of the thermal neutron flux in the EDELWEISS II dark matter direct search experiment

The results from measurements of thermal neutron flux in the EDELWEISS II experiment aimed at the direct detection of WIMPs (weakly interacting massive particles) by means of cryogenic germanium bolometers are described. Detailed knowledge of the neutron background is of crucial importance for the experiment, since neutrons with the MeV energy range of scattering seem to be hard to distinguish from the expected WIMP signal within the bolometers. Monitoring of the thermal neutron flux is performed using a mobile detection system with a low background proportional ³He counter. The neutron flux measurements were performed both outside and inside the device’s shielding, in the direct proximity of a cryostat with built-in germanium detectors. The sensitivity of the created thermal neutron detection system is on the level of 10⁻⁹ neutron (cm² s)⁻¹.     

EDELWEISS experiment: Direct search for dark matter

The EDELWEISS experiment is aimed at direct searches for nonbaryonic cold dark matter by means of cryogenic germanium detectors. It is deployed at the LSM underground laboratory in the Frejus tunnel, which connects France and Italy. The results of the experimentmade it possible to set a limit on the spin-independent cross section for the scattering of weak-interacting massive particles (WIMP) at a level of 10^?6 pb. Data from 21 detectors of total mass about 7 kg are being accumulated at the present time.     

Method for background reduction in an experiment devoted to WIMP searches with a liquid-xenon (liquid-argon) ionization chamber

A method for detecting ultraviolet photons from Xe ₂ ^* deexitation with an efficiency of nearly 100% is proposed. This method allows a reliable discrimination between Xe (Ar) recoil nuclei and background electrons. As a result, the β and γ background is almost completely suppressed. The neutron background can be reduced by water shielding and by selection of events involving only one recoil nucleus. The developed grid screen will remove the photon feedback. The small prototype TPC with a preliminary multiplication of ionization electrons in a proportional gap and a subsequent detection of the multiplied charges in the induction gap is constructed. The shape of an electron component of the proportional signal is obtained in this chamber for Penning mixtures. A chamber 636 mm long is now being prepared for WIMP searches. A background of about 10^?5 event/(keV kg d) can be obtained in this experiment.     

Results of dark matter search using the full PandaX-II exposure

We report the dark matter search results obtained using the full 132 ton·day exposure of the PandaX-II experiment, including all data from March 2016 to August 2018. No significant excess of events is identified above the expected background. Upper limits are set on the spin-independent dark matter-nucleon interactions. The lowest 90% confidence level exclusion on the spin-independent cross section is 2.2 × 10^?46 cm² at a WIMP mass of 30 GeV/c².     

Exclusion limits on the WIMP-nucleon cross section from the cryogenic dark matter search

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV/c2 WIMP mass and, at >75% C.L., the entire 3sigma allowed region for the WIMP signal reported by the DAMA experiment.     

Study on the Muon Backgroud in the Underground Laboratory of KIMS

KIMS is a group aiming at the search for WIMP. In WIMP search experiment, the muon is one important background. We measure the muon flux in Yangyang laboratory where is located at 700m underground. The structure and performance test of muon detector is described. The analysis on muon hit position and angle distribution has been performed. The simulations of muon flux have been done. The muon flux in the laboratory is found to be about (7.0±0.4)×10^-8/s/cm²/sr.     

Results of the pilot experiment to search for inelastic interactions of WIMPs with 73Ge

A pilot search for the excitation of ⁷³Ge to the first excited state at 13.26 keV by spin-dependent interactions of Weakly Interacting Massive Particles (WIMPs) was performed. The first experimental results have been analyzed with a new method. The background for these reactions is ≤0.0012 events/(keV kg(⁷³Ge) d). Although there is no theory for E2 excitations by WIMPs, this very large suppression of the background may promise an enlarged version of this experiment to be competitive. It is appropriate to propose an experiment with several kg of enriched ⁷³Ge detectors based on these results.     

Neutron Background from the (α, n) Reaction on 13C in the EDELWEISS-II experiment on direct search for weakly interacting particles of nonbaryonic cold dark matter

The purpose of the work is to evaluate the neutron background from an additional neutron source, the (α, n) reaction on ¹³C, in the polyethylene neutron shielding of the EDELWEISS-II experiment on the search for weakly interacting cold matter particles. The characteristic length of radon diffusion into polyethylene is obtained, the neutron energy spectrum is constructed, and the neutron flux from the (α, n) reaction is evaluated.     

Directional detection as a strategy to discover Galactic Dark Matter

Directional detection of Galactic Dark Matter is a promising search strategy for discriminating WIMP events from background. Technical progress on gaseous detectors and read-outs has permitted the design and construction of competitive experiments. However, to take full advantage of this powerful detection method, one need to be able to extract information from an observed recoil map to identify a WIMP signal. We present a comprehensive formalism, using a map-based likelihood method allowing to recover the main incoming direction of the signal and its significance, thus proving its Galactic origin. This is a blind analysis intended to be used on any directional data. Constraints are deduced in the (σn,mχ${\sigma }_n,m_{\chi }$) plane and systematic studies are presented in order to show that, using this analysis tool, unambiguous Dark Matter detection can be achieved on a large range of exposures and background levels.     

Upper limit on the cross section for elastic neutralino-nucleon scattering in a neutrino experiment at the Baksan Underground Scintillator Telescope

The results of a neutrino experiment that involved 24.12 yr of live time of observation of muons from the lower Earth’s hemisphere with the aid of the Baksan Underground Scintillator Telescope are presented. In the problem of searches for a signal from the annihilation of dark matter in the Sun, an upper limit on the cross section for the elastic scattering of a weakly interacting massive particle (WIMP) on a nucleon was obtained at a 90% confidence level from an analysis of data accumulated within 21.15 yr of live time of observation. A neutralino in a nonminimal supersymmetric theory was considered for a WIMP. The best limit at the Baksan Underground Scintillator Telescope on the cross section for spin-dependent neutralino interactionwith a proton corresponds to 3×10^?4 pb for the neutralino mass of 210 GeV/c ². This limit is three orders of magnitude more stringent than similar limits obtained in experiments that detected directly WIMP scattering on target nuclei.     

Dark matter results from 100 live days of XENON100 data

We present results from the direct search for dark matter with the XENON100 detector, installed underground at the Laboratori Nazionali del Gran Sasso of INFN, Italy. XENON100 is a two-phase time-projection chamber with a 62 kg liquid xenon target. Interaction vertex reconstruction in three dimensions with millimeter precision allows the selection of only the innermost 48 kg as the ultralow background fiducial target. In 100.9 live days of data, acquired between January and June 2010, no evidence for dark matter is found. Three candidate events were observed in the signal region with an expected background of (1.8 ± 0.6) events. This leads to the most stringent limit on dark matter interactions today, excluding spin-independent elastic weakly interacting massive particle (WIMP) nucleon scattering cross sections above 7.0 × 10(-45) cm(2) for a WIMP mass of 50 GeV/c(2) at 90% confidence level.     

First results from the XENON10 dark matter experiment at the Gran Sasso National Laboratory

The XENON10 experiment at the Gran Sasso National Laboratory uses a 15 kg xenon dual phase time projection chamber to search for dark matter weakly interacting massive particles (WIMPs). The detector measures simultaneously the scintillation and the ionization produced by radiation in pure liquid xenon to discriminate signal from background down to 4.5 keV nuclear-recoil energy. A blind analysis of 58.6 live days of data, acquired between October 6, 2006, and February 14, 2007, and using a fiducial mass of 5.4 kg, excludes previously unexplored parameter space, setting a new 90% C.L. upper limit for the WIMP-nucleon spin-independent cross section of 8.8x10(-44) cm2 for a WIMP mass of 100 GeV/c2, and 4.5x10(-44) cm2 for a WIMP mass of 30 GeV/c2. This result further constrains predictions of supersymmetric models.     

Dark matter search with the HDMS-experiment and the GENIUS project

We present a new Germanium Dark Matter Experiment. It consists of two HPGe-Detectors which are run in a unique configuration. The anticoincidence between the two detectors will further reduce the background that we achieve now in the Heidelberg-Moscow-Experiment and will allow to improve WIMP cross section limits to a level comparable to planned cryogenic experiments. This should also allow to test recently claimed positive evidence for dark matter by the DAMA experiment.We show first detector performances from the test period in the Heidelberg Low Level Laboratory and give a preliminary estimation for the background reduction efficiency. The HDMS experiment in being built up now in the Gran Sasso Underground Laboratory and will start taking data by the end of this year.For a substantial improvement of the WIMP-nucleon cross section limits, future dark matter experiments will have to be either massive direction-sensitive detectors or massive ton-scale detectors with almost zero background. A proposal for a high mass (1 ton) Ge experiment with a much further reduced background is the Heidelberg GENIUS experiment. GENIUS will be able to give a WIMP limit of the order 0.02 counts/day/kg and additionally to look for the annual modulation WIMP-signature by using raw data without subtraction.     

First results from the Cryogenic Dark Matter Search in the Soudan Underground Laboratory

We report the first results from a search for weakly interacting massive particles (WIMPs) in the Cryogenic Dark Matter Search experiment at the Soudan Underground Laboratory. Four Ge and two Si detectors were operated for 52.6 live days, providing 19.4 kg d of Ge net exposure after cuts for recoil energies between 10 and 100 keV. A blind analysis was performed using only calibration data to define the energy threshold and selection criteria for nuclear-recoil candidates. Using the standard dark-matter halo and nuclear-physics WIMP model, these data set the world's lowest exclusion limits on the coherent WIMP-nucleon scalar cross section for all WIMP masses above 15 GeV/c2, ruling out a significant range of neutralino supersymmetric models. The minimum of this limit curve at the 90% C.L. is 4 x 10(-43) cm2 at a WIMP mass of 60 GeV/c2.     

Status of an experiment aimed at laboratory searches for the electron-antineutrino magnetic moment at a level of μ ν ≤3±10− μ B

An experiment aimed at directly detecting antineutrino-electron scattering by using a 40-MCi tritium β-active source will make it possible to lower the present-day laboratory limit on the neutrino magnetic moment by two orders of magnitude. The experiment brings together novel unique technologies in studying rare processes of neutrino-electron scattering: (i) an artificial source of antineutrinos from tritium decay of 40-MCi activity with the antineutrino flux density of about 6×10¹⁴ cm^?2 s^?1 and (ii) new types of detectors capable of detecting electrons of energy down to about 10 eV, namely, a silicon cryogenic detector based on the ionization-into-heat conversion effect and a high-pure germanium detector with an internal signal amplification in the electric field. A compact installation located at a specially equipped underground laboratory (≤100 mwe) will provide favorable background conditions for running the experiment. With a background level of about 0.1 event/(kg keV d) and detector assembly masses of 3 and 5 kg for the silicon and germanium ones, respectively, a limit of μ _ν ≤3±10^? μ _B on the electron-antineutrino magnetic moment will be obtained within 1 to 2 years of data acquisition. The status of the experiment and the state of the art are presented.     

Dark matter experiment using Argon pulse-shape discrimination: DEAP-3600

DEAP-3600 is a single-phase liquid-argon dark matter detector that at time of writing is cooling down in preparation for filling at the SNOLAB facility near Sudbury, Ontario, Canada. DEAP-3600 is designed and constructed to achieve a sensitivity of 10^?46cm² for a WIMP-nucleon cross section for a 100 GeV WIMP. The steps taken in design and construction to achieve the ultra-low backgrounds required for such a sensitive WIMP search are reviewed.     

First dark matter results from the XENON100 experiment

The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso in Italy, is designed to search for dark matter weakly interacting massive particles (WIMPs) scattering off 62 kg of liquid xenon in an ultralow background dual-phase time projection chamber. In this Letter, we present first dark matter results from the analysis of 11.17 live days of nonblind data, acquired in October and November 2009. In the selected fiducial target of 40 kg, and within the predefined signal region, we observe no events and hence exclude spin-independent WIMP-nucleon elastic scattering cross sections above 3.4 × 10??? cm2 for 55 GeV/c2 WIMPs at 90% confidence level. Below 20 GeV/c2, this result constrains the interpretation of the CoGeNT and DAMA signals as being due to spin-independent, elastic, light mass WIMP interactions.